What does VEP involve?

Answered by: Dr Arun Mishra | Consultant Ophthalmic Surgeon, UK

Q:I have a 5 years old daughter. Whenever she falls ill, she seems to have a squint in one of her eyes. Even while she has fever, she seems to close her left eye. On consulting a doctor, we were told that there is loss of vision and were advised for patch treatment along with glasses. We were also advised for a test called VEP. On asking where to get this done, our doctor told us to consult a neurologist. The neurologist in turn asked us to go to an eye specialist. Can you please tell us what is VEP Test and where can this be done? Currently we are located in Hyderabad.

A:It seems that your daughter has a lazy eye also called amblyopia. This is common in children and is usually caused by refractive error or need for glasses from birth. There could be other causes as well. If the child can not see properly with one eye the brain switches off vision to suppress double vision, this then causes squint. When the child is fit and healthy, she can cope but when she is run down, she starts squinting. First thing your eye doctor should do is to test this by dilating drops (to dilate the pupils) and check whether she needs glasses & should be prescribed immediately and then only patching should be started to force the poor eye to improve. This is done with glasses and when she is using her eye for say watching TV, computer, games, books etc. for few hours daily preferably under supervision so that child does not cheat. If and when no obvious cause is found in the eyes, doctor requests VEP(Visual Evoked Potential). This is a test for brain with only electrodes on the scalp like EEG or ECG for heart. There is no need to worry about this and the test does not hurt or harm the child in any way. I would advise you to consult L V Prasad Eye Institute in Hyderabad. They should have this facility & expertise to do this there itself.
But the way you describe it, this test may not even be necessary and with adequate glasses and patching vision and squint should be improved. I want to create social awareness to test the vision of each child in India as early as possible but definitely by 3 years of age. After age 6 or so the vision can never be improved in life even with glasses and patching. This preschool test will not only detect poor vision for which treatment can be initiated early, successfully but also detect major eye diseases. Children themselves can only notice poor vision after starting school by which time it may be too late.